JP2006509113A - Multi-element airfoil for pulp screen - Google Patents

Abstract

The operation of the pulp screening apparatus 10 is improved by employing a multi-element foil 14. The foil 14 has a foil front section 22 and a foil rear section 24 that follows the section 22 at a distance, and one of the adjacent faces of both sections is on the pressure side 38 of the foil front section 22. Formed by one part and the other by the front end of the foil rear section 24. The adjacent surface forms an opposing wall of a fluid passage 42 for directing fluid flow from the pressure side 28 of the foil front section 22 to the camber low pressure side 34 of the foil rear section 24. The angle of attack α of the completed multi-element foil 14 is set to be significantly smaller than the angle of attack of the rear foil section 24, thereby increasing the negative pressure pulse generated by the rear foil section 24 and improving the operation of the screening device. .

Description

  The present invention relates to an improved screen device, and more particularly, the present invention uses a hydrofoil (as used in the paper industry) to suck pulp through the screen and to clean the screen. ) It relates to improved pulp.

  The use of a rotor with foil to generate pressure pulses by moving the foil past the screen and thereby clean the pulp screen is well known and has long been practiced in this industry. General technology. A pressure pulse, particularly a negative pressure pulse, cleans the aperture by creating a backflow that backflushes the fibers in the aperture. While this cleaning technique is reasonably effective, the maximum negative pressure pulse that a conventional foil or rotor can effectively generate is limited. Some specific examples of known techniques are described below.

  The pamphlet of WO 90/05807 (issued on May 31, 1990; PCT application PCT / SE89 / 00568), whose inventor is Lundberg et al., Discloses a general screening apparatus and (foil The use of wing elements on the rotor. The wing element has a front end of the wing in the direction of rotation closer to the screen than the rear end, and the wing has a dimension that is at least twice the radial dimension of the screen as measured in the direction of motion (circumferential); Thereby, the liquid which has already flowed to the outlet side through the screen is caused to generate a suction force to return to the inlet side through the screen, so that the pulp on the inlet side is diluted and the holes of the screen are washed.

  The pamphlet of WO 93/22494 (issued on 11 November 1993; PCT application PCT / FI / 00151), invented by Alajaski et al., Discloses a special pulse generator. The generator is configured to locally limit the pulse, thereby improving the cleaning operation of the pulse generator and thereby enhancing the screening effect.

  The pamphlet of WO 94/25183 (issued on Nov. 10, 1994; PCT application PCT / US94 / 04582) invented by Egan et al. Has a special part having a movable part protruding from the camber surface The use of an adjustable hydrofoil is disclosed. By adjusting the position of this movable part, an optimum spacing between the screen and the rotor is obtained, thereby improving the operation of the screening device.

  European Patent No. 0950754 by Alkawa (issued on October 20, 1998) applied liquid pressure to the screen adjacent to the front edge of the foil and negatively charged to clean the screen adjacent to the rear edge of the foil. A foil-type stirring device for applying pressure is disclosed.

  US Pat. No. 5,799,789, issued September 1, 1998 to Chen, specifically uses a conventional stirrer or foil and specially improves the operation of the screening system. It is taught to use a designed screen bar.

  Japanese Patent No. 93-243392 shows the use of an angular bar on the low pressure side of the screen to improve the operation of the screening device.

  In the aircraft industry, a high angle of attack without separation of air passing along the foil from the camber surface of the foil is achieved by using a multi-component camber type airfoil. As a result, the use of multi-element airfoil results in higher lift, which actually delays the start of flow separation (stall) from the foil, allowing higher angles of attack and increased camber To. The stall condition is delayed by passing air from the high pressure side of the wing or foil to the boundary layer on the wing low pressure side. This jet of air re-excites the boundary layer leaving the flow attached to the foil. Multi-element airfoils are typically used for aerodynamic applications.

  It is an object of the present invention to provide an improved foil for improving the efficiency of the screening process.

  Broadly speaking, the present invention relates to a pulp screening apparatus comprising a substantially cylindrical screen having a cylindrical axis, a foil, and means for attaching the foil to rotate about the cylindrical axis. Has a foil front section and a foil rear section, the foil front section being forward in the direction of movement of the foil as it rotates about the cylindrical axis, the foil rear section being spaced from the front. And located behind the front in the direction of motion, and is isolated from the rear end of the foil front section and the front end of the foil rear section to provide a space forming a passage for fluid, And each of the rear sections is adjacent to the high pressure side opposite the screen and adjacent to the screen opposite the screen. The front end of the foil rear section is located adjacent to a portion of the rear end of the foil front section, the portion of the pressure surface of the front foil and the rear of the foil rear section. The adjacent surface of the end forms the opposite wall of the passage, and the high pressure side of the front section of the foil, the opposite wall of the passage, and the low pressure side cambered in the rear section of the foil are relatively located So that fluid passing through the high pressure side of the foil front section flows through the passage along the rear camber low pressure side. The front foil section is set to the first angle of attack (α) and the rear foil section is set to the second angle of attack (θ).

The first angle of attack (α) and the second angle of attack (θ) are preferably different.
The second angle of attack (θ) is preferably larger than the first angle of attack (α).
The first angle of attack (α) is preferably 0 ° to 30 °, more preferably 5 ° to 15 °. The second angle of attack (θ) is preferably 0 ° to 60 °, more preferably 5 ° to 15 °.

  Preferably, the passageway has a substantially uniform width, measured parallel to the axis, opposite the width tapering from the passageway located at the intersection of the high pressure surface of the foil front section and the cavity. The minimum width (w) between the surfaces to be processed.

  Preferably, the minimum measurement width (w) is 0.1 to 5 centimeters (cm), more preferably 0.5 to 2 centimeters (cm).

  Preferably, the foil front section has a first length (x + y) measured along its camber surface and the foil rear section has a second length (z) measured along its camber surface. However, the ratio of both lengths will be in the range of 1 to 2 and 1 to 0.1, more preferably 1 to 1 and 1 to 0.25.

  Preferably, said portion includes a nesting cavity formed in the foil front section, in which the front end of the foil back section is received.

  Further features, objects, and advantages will become apparent from the following detailed description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

  FIG. 1 shows a conventional straight cylindrical pulp screen 10 having a cylindrical axis indicated by point 12. In the figure, the rotor is shown by a plurality of foils 14 that are mounted to rotate about axis 12 as shown schematically by arrow 16. As a conventional operation, pulp to be cleaned in the apparatus shown is introduced inside the screen 10 and the cleaned pulp passes through the screen 12 as indicated by the arrow 20 and is collected in the surrounding chamber 18. From there, it is sent to the next stage of work. Although arrow 20 indicates the preferred direction of flow, screens that work in reverse flow are also known, in which case chamber 16 becomes the inflow chamber and the screened pulp is collected inside screen 10. Although the present invention is applicable to any type of operation of pulp flow toward and away from axis 12, the embodiment disclosed herein is for pulp flow away from axis 12. A person skilled in the art can easily reverse the flow.

  The present invention can replace the conventional foil or rotor member normally employed in such screen rotors with a multi-element foil (MEF) of the type disclosed in detail below. The function of each foil 14 is that it can operate in a conventional manner to facilitate the screening operation. As previously mentioned, one of the main functions of the foil is to generate a negative pressure pulse at the trailing edge of the foil, thereby pulling the material back through the screen and cleaning the screen. The foil is also shaped to generate a positive pressure adjacent to the front edge of the foil, thereby driving the material past the screen. The foil 14 of the illustrated embodiment is configured so that pressure pulses are generated adjacent to the front end of the foil 14. The use of the MEF 14 of the present invention can increase the magnitude of the pressure pulse, particularly the magnitude of the negative pressure pulse at the rear end of the foil 14, thereby improving the operation of the screen.

  The embodiment of the invention shown in FIG. 2 is a MEF 14 having two foil sections, which MEF precedes in the direction of movement of the foil 14 as it rotates about the cylindrical axis 12 as indicated by arrow 16. It has a front section 22 and a foil rear section 24 that tracks section 22 in the direction of motion 16.

  The foil front section 22 has a camber surface 26 facing the screen 10 and an aerodynamically smooth surface 28 opposite the camber surface 26. The camber surface 26 following the front end 29 of the section 22 is contoured and oriented so that it approaches the screen 10 until the distance between the screen and the camber surface 26 reaches a selected minimum indicated by the reference numeral 30. The portion having the selected minimum value is located at a distance x from the front end 29 of the section 22 and a distance y from the rear end 32 of the section 22. The ratio of x / y will usually range from 1 to 10, preferably from 1 to 05.

  The foil rear section 24 is formed primarily to generate a suction (low) pressure on its camber (low pressure) surface 34. The camber surface 34 faces the screen 10, which aids in generating higher (low pressure) negative pressure pulses at the rear end 44 of the section 24. A flat or high pressure side (aerodynamically smooth) surface 36 forms the side of the foil rear section 24 opposite the screen 10.

  The cambers or shapes of the surfaces 26, 34 are each selected based on conventional design practices.

  The surface 28 adjacent to the rear end 32 of the foil front section 22 is formed to have a nesting portion 38 that is located between the front end 40 of the foil rear section 24 and the screen 10. The nesting portion 38 and the front end 40 are mounted relative to a rotor (not shown) such that a gap or passage 42 is formed therebetween, the opposing walls of this passage being the nesting portion 38 and the front end 40. And is formed by an adjacent surface. This passage 42 directs fluid flow from the flat or high pressure side of the foil front section 22 to the camber or low pressure side of the foil rear section 24.

  The length z of the camber surface 34 of the foil rear section 24, measured from the front end 40 to the rear end 44, is correlated with the length x + y of the surface 26. The gap between the two foils 22, 24, ending at the rear end 32, ie the position of the passage 42 (ie the relative dimensions of both foils) is adjusted before the flow along the camber surface 26 of the foil section 22 reaches the stall point It is selected to reach end 32. As is well known, the stall point is a complex function such as a foil shape and an angle of attack. In practice, the length z of the foil rear section 24 is about ½ to ¼ of the length x + y of the foil front section 22.

  It will be appreciated that the axial effective length (parallel to the axis 12) of the foil 14, ie, the foil front and back sections 22, 24, will be substantially the entire axial length of the screen. The most likely configuration would be a series of short foils 14 with an axial length that is only 1/4 or 1/3 of the total screen axial length. That is, a plurality of short axial length foils 14 arranged in a staggered configuration extend over the entire length of the screen 10. A full length foil 14 and / or a short section length multi-foil 14 configuration may be used.

  Accordingly, the passageway 42 also extends substantially the entire axial length of the screen 10, and substantially between the front end 40 and the adjacent wall of the nesting portion 38 of the face 28 of the foil section 22 in the axial direction of the foil 14. A substantially uniform spacing is maintained over the entire length.

  As can be seen from FIG. 2, the passage 42 tapers from the passage opening of the passage 42 adjacent to the front end 40 in the flow direction to a minimum width portion 41, the passage 42 being at this minimum dimension location, a portion 38 and a rear portion. There is a minimum width w between the adjacent surface 34 following the front end 40 of the section 24. This minimum width w is usually 0.1 to 5 cm.

  As is well known, the curvature of the nesting portion 38 is designed as follows. That is, fluid flowing along surface 28 is maintained to travel along portion 38 that forms one side of passage 42, and fluid flowing along portion 38 is inappropriate at or near minimum width point 41. Transfer to the surface 34 without generating turbulent flow and join the fluid flowing away from the surface 26 to assist in the transfer of the fluid, thereby allowing fluid flow along the surface 26 along the surface 34. Similarly, it is designed to smoothly transfer the flow from surface 26 (through the passage) to surface 34 so that it smoothly transfers to the flow. In fact, both foil sections 22, 24 are aerodynamic at both the front end 29, 40 and the rear end 32, 44 so as to prevent flow separation at the rear end 32 of the first foil. The trailing edge 44 is aerodynamic (acute angle) so that the flow along the surfaces 34, 36 is smoother, thereby reducing drag on the foil and the force required to rotate the rotor (foil 14). Is reduced. One form of camber that proved satisfactory was mathematically calculated and in the art as the National Aviation Advisory Committee (NACA) form, more specifically, the NACA 8421 air cut and reshaped into two airfoils. Known as foil.

  The foil front section 22 is adjustable in angle with respect to the radius leading to the front end 29 of the section 22, and also moves radially relative to the axis 12 as shown schematically by the arrow 50 to approach the screen 10. It can be attached to a rotor (not shown) so that it can be spaced apart. The foil rear section 24 can be adjustably attached as indicated by the arrow set 52. However, for a given installation, once the optimum position is determined, the placement and orientation of the sections 22, 24 are usually fixed.

  The angle of attack α of the foil 14 including the two foil sections 22, 24. The chord 54 that determines the angle of attack α extends from the front end 29 of the front section 22 to the rear end 44 of the rear section 24. That is, the angle of attack α of the foil 14 is the angle between the relative motion directions of the foil passing through the pulp, as indicated by the broken line 56.

  The angle of attack θ of the foil rear section 24 is determined by the angle between the chord 58 connecting the front end 40 and the rear end 44 of the camber surface 34 and the broken line 56 and is significantly different from the angle α.

  The angle θ is generally significantly greater than the angle α and is up to about three times larger. In some specific examples, for example, if the foil 14 has a zero angle of attack (α = 0 °), the angle of attack θ of the foil rear section 24 may also be zero (θ = 0). Thus, in some cases, α may be equal to θ (α = θ).

  The first angle of attack α (of the foil 14) is 0 ° to 45 °, preferably 5 ° to 15 °, and the second angle of attack θ (of the foil rear section 24) is 0 ° to 60 °, preferably 5 °. Will be ~ 25 °.

  In operation, the fluid flowing along the face 28 of the foil front section 22 flows along the face of the nesting portion 38 through the passage 42 between the portion 38 and the front end 40 of the foil section 24 and has a minimum width. Leaves portion 38 around point 41 and flows along camber surface 34 of foil rear section 24. The flow along this surface 34 stabilizes this flow as it flows over the surface 34 so that the angle of attack θ of the foil rear section 24 is typically that of a conventional single member foil. It can be significantly increased over that achieved. To ensure smooth fluid flow from the surface 28 into the gap or passage 42, the geometry of the nesting portion 38 of the surface 28 to prevent flow separation and reduce drag that causes excessive force consumption. Must be aerodynamic. The face of the portion 38 is designed to conform to the face shape of the front end 40 of the foil section 24 so that the foil sections 22 and 24 are simply joined together as will be described below with reference to FIG. It will be possible to operate as a single aerodynamic foil.

  In the case of FIG. 2, the shape of the surfaces 26, 28 adjacent the rear end 32 of the foil front section 22 and the shape of the surface 34 adjacent the front end of the foil rear section 24 facilitate the flow between the two foils. It is aerodynamic. In FIG. 3, the nesting portion 38 has been changed to a cavity-shaped aerodynamic configuration so that the passage 42A is more tortuous. This makes it difficult for the fluid to pass through the passage 42A according to the face portion 38A, but has the advantage that the entire airfoil 14 is more aerodynamically configured and reduces drag.

  As indicated, the portion 38A shown in FIG. 3 that extends from or forms the rear end of the pressure surface 28 of the foil front section 22 has been modified from that shown in FIG. A cavity defined by the portion 38A is adapted to receive the front end of the foil rear section 24, and in the embodiment of FIG. 2, the front end 40 and the surface 38 and the surface 34 form an opposing wall. The adjacent portion of the surface 34 forms one wall portion of the passage 42A, and the surface 38A forms an opposing surface of the passage 42A.

  Although the present invention has been described for a foil 14 comprised of two foil sections 22, 24, if necessary, more successive sections can be used, just as the multi-section foil is used in the aircraft industry. Could also be used.

  Although the invention has been described above, it will be apparent to those skilled in the art that modifications can be made without departing from the scope of the invention as defined in the claims.

1 is a schematic diagram of an axial direction of a pulp screening apparatus in which the present invention is incorporated. 1 is a schematic cross-sectional view showing a multi-element foil (MEF) of the present invention. FIG. 3 is a cross-sectional view similar to FIG. 2 but with the foil front section having an aerodynamically shaped cavity in which the front end of the foil rear section is received.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cylindrical pulp screen 12 Cylinder axis 14 Foil 16 Direction of rotation 18 Chamber 22 Foil front section 24 Foil rear section 26 Camber surface 28 Aerodynamic surface 29 Front end of foil front section 32 Rear of foil front section End 34 camber surface 38 nesting portion 40 front end of foil rear section 42 passage 44 rear end of foil rear section

Claims (12)

In a pulp screening apparatus comprising a substantially cylindrical screen having a cylindrical axis, foil, means for attaching the foil to rotate about the cylindrical axis,
The foil has a foil front section and a foil rear section, the foil front section being at the beginning of the direction of movement of the foil as the foil rotates about the cylindrical axis, the foil rear section Follow the direction of movement spaced from the front foil section so as to provide a space separating the rear edge of the front foil section and the front edge of the rear foil section; Form the passage of
Each foil section has a high pressure side facing away from the screen and a cambered low pressure side located adjacent to the screen facing the screen;
The pressure surface of the foil front section adjacent to the rear end of the foil front section has a portion adjacent to where the front end of the foil rear section is disposed, whereby the front of the foil front section The surface of the portion of the pressure surface and the adjacent surface of the front end of the foil rear section define an opposing wall of the passage;
The high pressure side of the foil front section, the opposing wall portion of the passage, and the camber low pressure side of the foil rear section are fluid passing through the high pressure side of the foil front section. Are arranged relative to flow along the camber low pressure side of the foil rear section,
The pulp screening apparatus, wherein the foil is set at a first angle of attack (α) and the rear section of the foil is set at a second angle of attack (θ).   The pulp screening apparatus according to claim 1, wherein the first angle of attack (α) and the second angle of attack (θ) are different.   The pulp screening apparatus according to claim 2, wherein the second angle of attack (θ) is larger than the first angle of attack (α).   The pulp screening according to claim 1, wherein the first angle of attack (α) is in the range of 0 ° to 45 °, and the second angle of attack (θ) is in the range of 0 ° to 60 °. apparatus.   The pulp screening according to claim 1, wherein the first angle of attack (α) is in the range of 5 ° to 15 °, and the second angle of attack (θ) is in the range of 5 ° to 25 °. apparatus.   The passage has a substantially uniform width as measured parallel to the axis and is tapered from the mouth of the passage at the intersection of the high pressure surface of the front section of the foil with the portion. And the minimum width (w) between the opposing surfaces. 5. A pulp screening apparatus according to claim 1 or claim 4.   The pulp screening apparatus according to claim 6, wherein the minimum width (w) is in the range of 0.1 to 5.0 centimeters (cm).   The pulp screening apparatus according to claim 6, wherein the minimum width (w) is in the range of 0.5 to 2.0 centimeters (cm).   The foil front section has a first length (x + y) measured along its camber surface and the foil rear section has a second length (z) measured along its camber surface The pulp screening apparatus according to claim 1, wherein a ratio of the first length to the second length is in a range of 0.5 to 10.   The foil front section has a first length (x + y) measured along its camber surface and the foil rear section has a second length (z) measured along its camber surface The pulp screening apparatus according to claim 1, wherein a ratio of the first length to the second length is in a range of 1 to 4.   11. The method of claim 1, wherein the portion has a nesting cavity formed in the foil front section, and the front end of the foil rear section is received in the nesting cavity. The pulp screening apparatus described in 1.   6. The pulp screening apparatus of claim 5, wherein the portion has a nesting cavity formed in the foil front section, and the front end of the foil back section is received in the nesting cavity.

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